Question

On heating the solids, the intermolecular space between molecules:
   (A) Increases
   (B) Decreases
   (C) remains same
   (D) depends on particles.

Answer 1

Hint: From kinetic theory of gases it's clear that kinetic energy is a function of temperature of a substance. Hence if we heat solids, it leads to the higher kinetic energy of particles and thus less intermolecular force of attraction.

Complete step by step answer:
 - As we know, on the basis of physical properties, matter can be classified into solids, liquids and gases. The particles of matter are in constant motion. Liquids have large intermolecular spaces and weak intermolecular flow. They do not have a definite shape. Gases have very weak intermolecular forces; high compressibility and they don’t have definite shape and volume.
 - In the case of solids, the intermolecular forces are very large and as a result the intermolecular spaces are very small. As a result, the molecules in a solid can vibrate about their mean positions, but cannot change their positions. It's because of this molecular arrangement, that solids have definite shape and definite volume.
 - The rigid nature of solids is due to this high intermolecular force of attraction. The solids are not much compressible because of the absence of space between the molecules.
 - The phase of a substance depends on the balance between the intermolecular forces and the kinetic energy of the individual particles. The kinetic energy is a function of the temperature of the substance and keeps the molecules apart and moving around. Hence, the increase in kinetic energy of individual atoms is because of the increase in temperature.
 - As we mentioned, in a solid, the atoms or molecules are closely packed together. On heating, their kinetic energy pushes neighboring atoms or molecules apart from each other. This pushing of atoms or molecules results in a slightly increased distance, on average between atoms or molecules , and thus it adds up to a greater size for the whole body of solids. Thus, an increase in temperature will increase the size of a solid by a certain fraction in every dimension.
- This implies that on heating solids, intermolecular forces are becoming weak and intermolecular space increases. So, the correct answer is “Option A”.

Note: The change in the size of a body in terms of length, area or volume, as a result of change in temperature can also be described as thermal expansion. Thermal expansion is not negligible but relatively small for liquids and solids and is large for gases. The change in temperature can be associated with phase transitions such as melting, boiling, and subliming.